This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Our work at NE-CAT has focused on a number of metalloenzyme systems for which crystal quality and size make their study difficult at other synchrotron sources. A key project in the lab focuses on the binuclear manganese metalloezyme arginase, as well as enzymes that share the arginase fold such as the zinc enzymes human histone deacetylase-8 and bacterial acetylpolyamine amidohydrolase. Comparisons of these metalloenzymes will ultimately reveal the chemical and structural basis for the divergent evolution of metal ion specificity and stoichiometry in the arginase fold. Additionally, our work at NE-CAT has focused on terpenoid cyclases. These are metal-requiring enzymes that catalyze the most complex organic chemical reactions in biology. Specifically, our work has focused on sesquiterpene cyclases that catalyze cyclization reactions involving the substrate farnesyl diphosphate: germacradienol synthase and delta cadinene synthase.